An organization for the Karen ethnic minority group in Myanmar says more than 3,000 residents have fled to neighboring Thailand due to military airstrikes.
The organization made the announcement on Sunday, urging the military to stop its air raids.
Myanmar's state-run TV reported on Sunday night that a militant force attacked a military post in breach of a ceasefire agreement. It was seen as an admission that the military suffered the attack on Saturday by an armed group from the southeastern state of Karen.
The media outlet added the military will take necessary actions, an indication that it has been retaliating.
A growing number of armed members from ethnic minority groups in Myanmar have been helping demonstrators protest the February 1 coup.
They have been responding to calls for help from the Committee Representing the Pyidaungsu Hluttaw, which includes members of the National League for Democracy party led by Aung San Suu Kyi. She is among those detained by the military.
The military has been cracking down on protesters. Local media report that five people were killed on Sunday after 114 others lost their lives on Saturday, Armed Forces Day, marking the highest single-day death toll since the coup.